1. Field of the Invention
The present invention relates to the field of cancer chemotherapy. More particularly, the present invention relates to a method for improving the effectiveness of cancer chemotherapy by preventing, reducing, or reversing the development of cellular resistance to chemotherapeutic agents, i.e., the phenomenon known as "multidrug resistance" (MDR), during the course of therapy. This is achieved by administering to patients N-alkyl-1,5-dideoxy-1,5-imino-D-glucitol or galactitol compounds ("iminosugars") in conjunction with chemotherapeutic drugs.
2. Description of Related Art
Multidrug Resistance (MDR)
Multidrug resistance, the phenomenon whereby primary exposure of tumor cells to a single chemotherapeutic drug results in cellular resistance to multiple drugs, is believed to be the basis for tumor cell survival (Bradley et al. (1988) Biochim. Biophys. Acta 948:87-128). MDR is manifested as a simultaneously acquired cellular resistance to several cytotoxic substances, which can be surprisingly structurally and functionally unrelated, and is often observed after prolonged exposure of cells to anticancer drugs of the "multidrug resistance group." The latter includes such different compounds as actinomycin D, mitomycin C, anthracyclines, colchicine, rhodamine, ethidium bromide, doxorubicin, epipodophyllotoxins, paclitaxel, taxol, reserpine, and the vinca alkaloids. Exposure of cells to one of these drugs can lead not only to specific resistance to this drug, but also to non-specific cross-resistance to all the other drugs of the MDR group.
Study of this phenomenon has focused on a number of different possible biological mechanisms. Volm et al. ((1993) Cancer 71:2981-2987) and Bradley et al. ((1994) Cancer Metastasis Rev. 13:223-233) have investigated the overexpression of P-gp, a plasma membrane glycoprotein believed to rapidly efflux MDR-type drugs, thus protecting cells from damage by preventing these drugs from reaching their intracellular targets. Doige et al. ((1993) Biochim. Biophys. Acta 1146:65-72) and Wadkins et al. ((1993) Biochim. Biophys. Acta 1153:225-236) have studied the role of lipids in MDR. While differences in the glycerolipid and sphingomyelin compositions of MDR and drug-sensitive cells have been observed (Holleran et al. (1986) Cancer Chemother. Pharmacol. 17:11-15; Ramu et al. (1984) Cancer Treat. Rep. 68:637-641; May et al. (1988) Int. J. Cancer 42:728-733; Welsh et al. (1994) Arch. Biochem. Biophys. 315:41-47; Wright et al. (1985) Biochem. Biophys. Res. Commun. 133:539-545), and the ganglioside composition of MDR and drug-sensitive cells has been investigated, no clear picture as to the basis of drug resistance emerged from these studies.
More recently, Lavie et al. ((1996) J. Biol. Chem. 271:19530-10536) demonstrated a correlation between the cellular content of glycosphingolipids and MDR. These workers demonstrated that tamoxifen, verapamil, and cyclosporin A, agents that reverse multidrug resistance, as well as 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol, an inhibitor of glucosylceramide synthesis, decrease glucosylceramide levels in an MDR human breast cancer cell line that accumulates high levels of glucosylceramide compared with the parental wild-type, drug-sensitive cell line (Lavie et al. (1997) J. Biol. Chem. 272:1682-1687). They concluded that high cellular levels of glucosylceramide are correlated with MDR, and that glycolipids are therefore a target for the action of MDR-reversing agents.
1,5-dideoxy-1,5-imino-D-glucitol and galactitol Compounds
1,5-dideoxy-1,5-imino-D-glucitol (also known as 1-deoxynojirimycin, DNJ) and its N-alkyl derivatives are known inhibitors of the N-linked oligosaccharide processing enzymes .alpha.-glucosidase I and II (Saunier et al., J. Biol.Chem. (1982) 257:14155-14161 (1982); Elbein, Ann. Rev. Biochem. (1987) 56:497-534). As glucose analogs, they were also predicted to have the potential to inhibit glucose transport, glucosyltransferases, and/or glycolipid synthesis (Newbrun et al., Arch. Oral Biol. (1983) 28: 516-536; Wang et al., Tetrahedron Lett. (1993) 34:403-406). Their inhibitory activity against glucosidases has led to the development of these compounds as anti-hyperglycemic agents and antiviral agents. See, for example, PCT International Publication WO 87/03903 and U.S. Pat. Nos. 4,065,562; 4,182,767; 4,533,668; 4,639,436; 4,849,430; 4,957,926; 5,011,829; and 5,030,638. N-butyl DNJ is an inhibitor of HIV replication in vitro (Fleet et al. (1988) FEBS Lett. 237:128-132; Karpas et al. (1988) Proc. Natl. Acad. Sci. USA 85:9229-9233). This compound has been clinically evaluated as a potential AIDS therapeutic (Jacob et al. (1992) in Natural Products as Antiviral Agents, C. K. Chu et al., Eds., pp. 137-152, Plenum Publishing Co., N.Y.), and has been found to exhibit little cytotoxicity in vitro (Platt et al. (1992) Eur. J. Biochem. 208:187-193).
Platt et al. ((1994) J. Biol. Chem. 269:8362-8365) have demonstrated that certain N-alkylated derivatives of DNJ inhibit the glucosyltransferase-catalyzed biosynthesis of glucosylceramide, resulting in the inhibition of biosynthesis of all glucosylceramide-based glycosphingolipids. Glycolipids constitute an important class of glycoconjugates found in the membranes, and particularly the plasma membrane, of eukaryotic cells. These authors speculated that these N-alkylated derivatives specifically inhibit UDP-glucose-N-acylsphingosine glucosyltransferase (EC 2.4.1.80). This transferase generates glucosylceramide (GlcCer), the precursor for the more complex glycosphingolipids and gangliosides. Platt et al. also demonstrated that N-butyl DNJ inhibited glycolipid expression at the cell surface. The authors suggested that N-alkylated DNJs would be useful in treating lysosomal glycolipid storage disorders such as Gaucher's disease.
In a subsequent paper, Platt et al. showed that the galactose analogue of N-butyl DNJ, i.e., N-butyl-deoxygalactonojirimycin (N-butyl DGJ), is a more selective inhibitor of glycolipid biosynthesis, only weakly inhibiting the N-linked oligosaccharide processing enzymes .alpha.-glucosidases I and II, and not inhibiting lysosomal .beta.-glucocerebrosidase (which is required for the cleavage of GlcCer to glucose and ceramide). N-butyl DGJ was shown to be comparable to N-butyl DNJ as an inhibitor of UDP-glucose-N-acylsphingosine glucosyltransferase and in preventing lysosomal glycolipid storage in an in vitro model of Gaucher's disease.
In 1997, Platt et al. (Science 276:428-431) reported the prevention of glycosphingolipid lysosomal storage in a mouse model of Tay-Sachs disease using N-butyl DNJ. This disease is characterized by a deficiency in the A isoenzyme of .beta.-hexosaminidase, which degrades G.sub.M2 ganglioside. A deficiency of this enzyme in humans results in accumulation of G.sub.M2 ganglioside in brain cell lysosomes, leading to severe neurological degeneration. The authors noted that this compound is water soluble and noncytotoxic over a broad range of concentrations in vitro and in vivo. Oral administration to healthy mice resulted in glycosphingolipid depletion in multiple organs without causing any overt pathological side effects. In Tay-Sachs mice, no toxicity to N-butyl DNJ was observed based on visible inspection and observation of the animals, and of organ weights at autopsy. While spleen and thymus tissues were 50% acellular, no immunocompromization was apparent. The authors concluded that in this in vivo mammalian model, oral treatment with N-butyl DNJ is well tolerated, and effectively inhibits glycosphingolipid biosynthesis and subsequent accumulation in brain cell lysosomes.
Treatment of MDR
Many chemosensitizers have been reported to antagonize MDR in in vitro systems, and some have been shown to be effective in viva when coadministered with appropriate chemotherapeutic agents to nude mice bearing multidrug-resistant tumors. Unfortunately, success in the laboratory has not necessarily translated to success in the clinic. Dose-limiting side effects of first-generation MDR modulators have been observed. Low therapeutic indices and failure to achieve therapeutic blood levels have also been problematic (Dalton et al. (1995) Cancer 75:815-20; Tsuro et al. (1981) Cancer Res. 41:1967-72; Ries et al. (1991) Med. Oncol. Tumor Pharmacother. 9:39-42; Chabner (1991) J. Clin. Oncol. 9:4-6; Raderer et al. (1993) Cancer 72:3553-63; Mulder et al. (1996) J. Exp. Ther. Oncol. 1:19-28; Fischer et al. (1995) Hematol. Oncol. Clin. North Am. 9:363-82; Wishart et al. (1994) J. Clin. Oncol. 9:1771-77). In addition, patient dosing is sometimes complicated by pharmacokinetic drug interactions, resulting in increased plasma concentrations or decreased elimination of cytotoxic drugs, resulting in increased toxicity (Egorin et al. (1996) Proc. Am. Soc. Clin. Oncol. 15:473; Beketic-Oreskovic et al. (1995) J. Natl. Cancer Inst. 1593-602.88). Most of the results from MDR-reversal trials have been disappointing, except for those for some hematological cancers (Chabner (1991) J. Clin. Oncol. 9:4-6; Raderer et al. (1993) Cancer 72:3553-63; Mulder et al. (1996) J. Exp. Ther. Oncol. 1:19-28; Fischer et al. (1995) Hematol. Oncol. Clin. North Am. 9:363-82).
Thus, a common, major obstacle to cure with chemotherapeutic agents is the survival and continued proliferation of cells that are resistant to further treatment. MDR is therefore a formidable impediment to successful chemotherapy. The art continues to seek agents that can be used to prevent or reduce this phenomenon during cancer chemotherapy. The use of N-substituted-imino-D-glucitol or galactitol derivatives in conjunction with chemotherapeutic agents for preventing or reducing the extent of MDR during chemotherapy has not, as far as the present inventor is aware, been previously disclosed or suggested.